1. Field of the Invention
This invention relates to a power-supply circuit device, specifically, to a power-supply circuit device using an IC packaging improved in the shape of leads led out from a main packaging body.
2. Description of the Related Art
As widely known, IC (integrated circuit) packaging in which an IC chip and leads (lead pins) are connected by wire bonding or the like and packaged in a main packaging body made of a resin has been employed.
FIGS. 2(A)-2(C) show, as an example, a conventional IC packaging with five lead pins. FIG. 2(A) is a top view, FIG. 2(B) is a sectional view along line B—B of FIG. 2(A), and FIG. 2(C) is a side view viewed from the arrow direction shown in FIG. 2(B).
In a monolithic IC, a composite device or the like, which includes a power MOSFET (metal-oxide-semiconductor field effect transistor) 11, because an IC 12 is mounted on the power MOSFET 11, five lead pins with even pin-pitch intervals (d3) are generally used. As shown in FIG. 2(A), on one side wall of this main packaging body 13, five lead pins 14 are provided. In this case, a third pin 14c at the center is connected to a drain terminal of the MOSFET 11, a fifth pin 14e is connected to a source terminal of the MOSFET, and a first pin 14a, a second pin 14b, and a fourth pin 14d are connected to corresponding control terminals of the IC 12. Normally, since a high voltage is applied to the drain terminal of the MOSFET 11 and the source terminal is grounded, the voltage difference between the terminals is extremely large. Therefore, the third pin 14c and fifth pin 14e are used so that the lead pins 14 are not adjacent.
FIG. 2(B) shows a forming of this packaging. As shown in the drawing, the first pin 14a, third pin 14c and fifth pin 14e are bent upward, whereby separation distances from the adjacent second pin 14b and the fourth pin 14d are increased (see FIG. 2(C)). This method is used when an IC packaging having such a structure is mounted on a circuit board surface by soldering so as to suppress occurrence of a short circuit between adjacent lead pins and occurrence of solder bridging when an IC packaging is solder-jointed on a printed circuit board.
In general, for convenience of assembly, lead pins are arranged at even intervals (d3), and the back surface of an internal device is connected to the central pin. Namely, in a case of a power MOSFET, a drain electrode on its back surface is directly fixed by a conductive adhesive. Conventional power MOSFET packaging structures are of a three-pin structure and have sufficient separation distances between a terminal (central terminal), to which the drain receiving a high voltage is connected, and other adjacent terminals. However, in a monolithic integrated circuit, a composite device or the like, which includes a power MOSFET as described above, because the IC is mounted on the power MOSFET, five lead pins with even intervals are generally used. In this case as well, the center third pin is connected to the drain electrode of the power MOSFET. Therefore, when a power MOSFET having a high withstand voltage, such as 800V, is mounted, sufficient separation distances between the central third pin and other adjacent pins cannot be secured with the conventional lead pin structure that includes lead pins separated by even intervals. Namely, when an IC packaging of such a structure is mounted on a circuit board surface by soldering, if the separation distances between the third pin receiving a high voltage and adjacent second and fourth pins are small, a short circuit due to dusts or the like easily occurs. Furthermore, when an IC packaging is solder-jointed on a printed circuit board, solder bridging easily occurs since solders spread wider than the distances between lead pins. For example, if the operating voltage is 700V, the separation distances need to be 1.9 mm. Thus, in the conventional structure, if the separation distances are about 1.7 mm, safety standards may not be satisfied even with the forming of bending lead pins in the up-and-down direction. In short, in the conventional lead pin structure, the separation distances cannot be sufficiently secured.
Furthermore, in the conventional packaging, since a header 14h part, which forms an integral part with the third pin and connected to the drain electrode receiving a voltage as high as 800V, is configured to exposed, product handling is not safe.